In geothermal power plants, hot fluid from a geothermal resource is extracted via a production well from underground to the ground surface. The extracted hot fluid is used for power production either directly when converted to steam and expanded in a turbine, or indirectly by means of a binary cycle power plant whereby the extracted hot fluid is brought in heat exchanger relation with the motive fluid of the power plant, such as an organic motive fluid. The heat depleted geothermal liquid is returned underground via an injection well, which is separated from the production well. The injected geothermal liquid becomes reheated and makes its way back to the production well.
As a result of continuous exploitation of the geothermal resource, the enthalpy of the extracted fluid and/or pressure tends to decrease over the course of time, reducing the economic viability of a power plant for producing power from the extracted geothermal resource. It would therefore be desirable to provide a method for enhancing a production well or injection well drilled in or adjacent to a field containing a depleted geothermal resource.
US 2012/0181034 discloses a method for stimulating an underground reservoir formation by introducing a particulate diverting agent into a well, to thereby temporarily seal passages within a fracture near the wellbore face and to isolate the fracture from the well. When a stimulation fluid is applied to the well at a sufficient pressure, an additional fracture is produced by hydroshearing such that it is expanded under shear. Rather than causing permanent damage to the permeability of the fractures which will lead to a reduction in economic value of the geothermal resource, the particulate diverting agent is able to degrade over an extended time. One disadvantage of this stimulation method is that it is a one-time operation due to the degradation of the diverting agent.
Another drawback of this stimulation method relates to its unpredictability. At times, a fracture will be produced at that unknown subterranean region which is not necessarily to best depth for use in such a developed well.
It is an object of the present invention to provide a method for stimulating a geothermal well by reopening a fracture extending thereto within a rock formation at a selected depth.
It is an additional object of the present invention to provide a method for stimulating a geothermal well that is repeatable for a plurality of stimulation operations.
It is a further object of the present invention to advantageously provide a method for stimulating an injection/production wells so that the amount of power that can be generated from the geothermal fluid can be increased.
Other objects and advantages of the invention will become apparent as the description proceeds.